Pre-mixing combustion chambers are low-pollutant gas turbine combustion chambers. Gas turbines can be utilized both stationary mechanisms such as generator drives in power plants, as well as in aircraft engines. Maximum limits for nitrogen oxide emission of stationary gas turbines have been set in numerous industrialized countries. Since corresponding recommendations also exist for aircraft engines, great significance is accorded to the reduction of nitrogen oxide formation in the combustion chambers in the framework of reducing pollutant emissions. Rich/lean combustion ratios wherein the combustion ensues with a first, rich stage and a second, lean stage with air excess is currently utilized for reducing nitrogen oxide in aircraft engines.
Compared thereto, even greater reductions can be achieved with the pre-mixed lean combustion applied in stationary gas turbines. Since the nitrogen oxide formation increases with, among other things, the highest temperature, methods have been developed to lower the highest flame temperature. A distinction is thereby made between wet and dry methods. In the previously predominantly employed, wet methods, water or water vapor are introduced into the combustion zone separately or pre-mixed with the fuel. It is thereby disadvantageous that processed water is required, the consumption thereof also being high. Over and above this, the system efficiency drops given the wet methods.
Due to these disadvantages, dry methods wherein the excess air coefficient in the combustion zone is increased as far as possible and air and fuel are entirely or partially pre-mixed are increasingly desired. In order to meet the legal regulations and recommendations, air and fuel must be mixed as uniformly as possible preceding the combustion chamber. The peak temperatures in the flame can be reduced in this way by itself. To this end, pre-mixing combustion chambers have been developed wherein a specific length of the pre-mixing chamber or a minimum dwell time in the pre-mixing chamber is needed in order to achieve a high degree of homogeneity. However, there is thereby the risk that the fuel/air mixture will ignite in the pre-mixing chamber. Since the blending process is not completed in this case, high temperatures that lead to increased nitrogen oxide formation arise locally as a consequence of inhomogeneities. Further, there is the risk of a flashback from the combustion zone into the pre-mixing chamber. In order to avoid this, paddle grids or the like are attached at the end of the pre-mixing chamber given traditional pre-mixing chambers in order to accelerate the mixture and produce a twist. When a flashback nonetheless occurs, this leads to damage or destruction of combustion chamber parts such as, for example, the paddle grid.
In a known combustion chamber arrangement according to German Letters Patent 43 18 405, a reduction of the nitrogen oxide formation is enabled with pre-mixed lean combustion without risk of self-ignition in a pre-mixing path in that the fuel is injected into a pre-mixing chamber fashioned essentially straight that tangentially discharges into an essentially rotationally-symmetrically fashioned combustion chamber, as a result whereof a creation of twist is achieved when the mixture flows in. Since the twisting is not generated with additional component parts such as paddle grids, the risk of parts damage given a potentially occurring flashback is eliminated. An adequate combustion stability is assured with a supporting pilot combustion that ensues in a separate combustion zone. The hot gasses from the pilot zone are mixed into the lean main zone, whereby the stabilizing effect is highly dependent on the existing flow field and can be subject to greater fluctuations in different operating conditions. Moreover, the flow from the main combustion zone into the after-combustion zone is deflected by 90.degree., which leads to an increased pressure loss.
Therefore, there is a need for a pre-mixing combustion chamber of the species initially described wherein the stabilizing effect of the pilot combustion is improved.